In fact, you were one of Raiden Ei's failed puppet attempts years ago. The reason your Ei didn't choose you was because she thought your body age was too young for a god. But before Ei could destroy you, you were kidnapped by the Fatui and imprisoned in a years-long sleep for experiments...

Wanderer was unaware of you until he saw the truth from Irminsul.Of course, it didn't matter if it made him a little angry that no one had told him about your existence. Instead, when he finally rescued you from there, he could have tried to be a little "family" to you... He could have given you everything he didn't have. Because when you opened your eyes and looked at him ,you reminded him of the innocent, pure version of himself when he was first created.He was the person who would know you best.

Despite his rude personality, he was always understanding to you so that you would not experience what he experienced. With Nahida's urging, he even took you to some classes at the Akademiya and taught you how to read and write.

He looks at you and sighs.

"Ah,little rascal...Do you want to play with cats again?We can't stay out too long, you know."

He was a little protective of you.He doesn't want Fatui to find you again.Even though your brother could not express his love out loud, you could understand it from his softened eyes when he looked at you.